Field of the Invention
The present invention relates to a feed additive for fish cultivation and more particularly it relates to an improvement of the productivity of fish cultivation by promoting digestion and absorption of nutrients included in feeds.
The growth of fish depends on the quality and quantity of the feed used, and in fish cultivation, a technique is required whereby a lot of fish are raised most efficiently within a restricted water area. Recently the output of cultivated fish has increased surprisingly, and with the resultant increment in the quantity of feed consumed, studies on assorted feeds have progressed and ways to use a feed more effectively have been investigated.
Protein, which is an essential nutrient for growth of animals and maintenance of life, participates in the composition of each tissue in the animal body, and also plays an important role as a component of enzymes and hormones. Fish, in general, have a high nutritional requirement for protein (2-4 times the requirement for live stock) and, on the other hand, have a low digestive and metabolic ability toward carbohydrate, so that they have high dependency on protein as an energy source. In many cases, therefore, the assorted feed for fish cultivation contains proteins in an amount of about 40-45%, about 2 to 2.5 times more than that for domestic animals.
The assorted feed for fish cultivation is dependent for protein raw material mainly upon animal protein resources, but the capacity of such resources has its limit. Hence, although it is desired to find new protein resources for the long term, to solve the present problem, studies have been required to determine the best means for the effective utilization of protein resources which are used today as a feed.
When fish meal, which has been the principal animal protein raw material in assorted feeds for fish cultivation, is compared with raw food, the former is considered to be inferior to the latter with respect to the rate of growth of fish, although there is little difference in the analysis of the nutritional constituents between the two feeds. The reason for the inferiority of fish meal is that the digestion rate, or the rate at which the feed is digested and absorbed by fish is low. An improvement in the digestion rate, therefore, would signify the more effective utilization of protein resources.
Furthermore, to allow proteins to be used as a substantial growth promoting factor, which is an original function, it is important that lipids present be effectively utilized as an energy source.
Attempts to improve the digestion rate of nutrients by adding a digestive enzyme to the assorted feed for fish cultivation have been made since the 1960s and some effects have been confirmed, but further technical developments are necessary for their practical use.